The roles water in living organisms and water as a habitat for organisms

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Michael Osgood                                                                         2/10/2

The roles water in living organisms and water as a habitat for organisms

Introduction

Water is the most abundant liquid on the planet. It covers 2/3rds of the earth’s surface, and at least 60% of living organisms is water. This value may be as large as 99% - in a jellyfish. The reason for such a large amount of water making up organisms is the fact that it is a major cell constituent – more on that later.

Water is a simple molecule yet has many interesting properties which contribute to its importance.

Structure

Water is made up of two hydrogen atoms bonded to one oxygen atom. They are covalently bonded and the intramolecular covalent bonds are very strong. The structure is non-linear, due to the electron pair repulsion of the two lone pairs of electrons on the oxygen atom.

Major cell constituent

Often 2/3rds or more of living cells are water. The water is found mainly in the cytoplasm, and it plays a vital role in many functions of the cell: in all organisms – metabolism, and in plants photosynthesis and support. The actual roles of water in these functions are described more fully later.

Polar solvent / universal solvent

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The pulling of the electrons towards the O makes the O electropositive and the H’s electronegative. As opposites attract, not only are the hydrogen atoms attracted to their O atom electrostatically, but also to the O atoms in neighbouring molecules. These bonds are called hydrogen bonds, and are responsible for the great strength and unexpectedly high melting and boiling points of water.

The diagram above shows the differing electronegativities, and it is for the polar nature of this molecule that water is such a good solvent. More substances than any other can dissolve in it, and it has been ...

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